3GPP that is a standardization group of W-CDMA is studying a communication scheme that becomes a successor to W-CDMA, HSDPA and HSUPA, that is, 3GPP is studying Long Term Evolution (LTE). As radio access schemes, OFDM (Orthogonal Frequency Division Multiplexing) is being studied for downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) is being studied for uplink (refer to non-patent document 1, for example).
OFDM is a scheme for dividing a frequency band into a plurality of narrow frequency bands (subcarriers) so as to perform transmission by carrying data on each subcarrier. By arranging the subcarriers on frequencies densely without interfering with each other while a part of them overlap, high speed transmission is realized so that efficiency of use of frequency increases.
SC-FDMA is a transmission scheme that can decrease interference among terminals by dividing frequency band and performing transmission using frequency bands that are different among a plurality of terminals. Since the SC-FDMA has characteristics that variation of transmission power becomes small, low power consumption in the terminal and wide coverage can be realized.
LTE is a system in which a plurality of user apparatuses share one or more physical channels in the uplink and the downlink for performing communication. The channel shared by the plurality of user apparatuses is generally called a shared channel. In LTE, the channel is the Physical Uplink Shared Channel (PUSCH) in the uplink, and is the Physical Downlink Shared Channel (PDSCH) in the downlink.
In the communication system using the above-mentioned shared channel, it is necessary to signal information indicating which user apparatus is assigned the shared channel for each subframe (1 ms in LTE). In LTE, a control channel used for the signaling is called Physical Downlink Control Channel (PDCCH) or called Downlink L1/L2 Control Channel (DL L1/L2 Control Channel). Information of the physical downlink control channel includes, for example, downlink (DL) scheduling information, acknowledgement information (ACK/NACK), uplink (UL) scheduling grant, overload indicator, transmission power control command bit and the like (refer to non-patent document 2, for example).
The DL scheduling information and the UL scheduling grant correspond to the information for signaling which user apparatus is assigned the shared channel. The DL scheduling information includes, for example, assignment information of resource blocks in downlink, ID of UE, the number of streams, information on precoding vector, data size, modulation scheme, information on HARQ (hybrid automatic repeat request), and the like with respect to the downlink shared channel. The UL scheduling grant includes, for example, assignment information of resource blocks in uplink, ID of UE, data size, modulation scheme, uplink transmission power information, demodulation reference signal in uplink MIMO, and the like with respect to the uplink shared channel.
In the L1/L2 control channel of the E-UTRA, it is being discussed to define a plurality of sets of modulation and coding (MCS (modulation and coding scheme) set (combinations of modulation scheme and channel coding scheme)), and to change the MCS set according to a position and propagation loss of a user apparatus (UE: User Equipment) which is performing communication in the cell. More particularly, when the propagation loss of the UE is large, a low coding rate and a low modulation multilevel number are used. Accordingly, even when the propagation loss is large, it becomes possible to ensure the quality of the L1/L2 control channel.    [Non-patent document 1] 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006    [Non-patent document 2] R1-070103, Downlink L1/L2 Control Signaling Channel Structure: Coding